Manufacturing of semiconductor devices typically involves performing a sequence of procedures with respect to a substrate, such as silicon substrate, glass plate, etc. These steps may include polishing, deposition, etching, photolithography, heat treatment, and so forth. It is generally the case that other processes are required to be performed at other processing locations within a fabrication facility, and it is therefore necessary to transport the substrates within the fabrication facility from one processing location to another. Depending upon the type of semiconductor device to be manufactured, there may be a relatively large number of processing steps required to be performed at a considerable number of different processing locations within the fabrication facility.
Substrates are conventionally transported from one processing location to another within substrate carriers such as sealed pods, cassettes, containers and so forth. It is also conventional to employ automated container transport devices, such as automatic guided vehicles (AGVs), overhead transport (OHT) systems, container handling robots, etc., to move containers from location to location within the fabrication facility.
Overhead conveyor delivery of wafer containers, such as front-opening unified pods (FOUPs), in a semiconductor fabrication facility (fab) has many advantages over hoist delivery due to the complexity of OHT vehicle management. However, transferring FOUPs from the conveyor to a tool load port currently requires multiple mechanisms. These mechanisms reduce container throughput in the fab as well as add cost and complexity to the container transfer system.
A conventional ceiling mounted conveyor travels down the length of a tool bay. Lift mechanisms are located along the conveyor for raising a FOUP off the conveyor. Port loading mechanisms remove FOUPs from the lift mechanism to a port or shelf located to the side of the conveyor. After the FOUP has been removed from the conveyor, other FOUPs traveling on the conveyor may then resume travel on that section of conveyor. And at some later time, a mechanism will transfer the FOUP from the port or shelf to a tool load port. A second FOUP cannot be removed from the conveyor and placed on the same port until the port has been cleared (e.g., the first FOUP must be moved from the port to a tool load port). A tool bay often requires multiple sets of lift mechanisms and ports to prevent the possibility of having all ports full at the same time. If this happens, traffic on the conveyor will stop until there is a place to unload a waiting FOUP, resulting in the conveyor being congested with FOUPs.
Conventional FOUP conveyor buffers are either first-in-first-out (FIFO), first-in-last-out (FILO), or require shifting all FOUPs (e.g., circular buffer) to retrieve one FOUP. Each of these conveyor buffers allows a FOUP, only in one designated location, to be accessed by a container transport device. The transport device often sits idle while waiting for another FOUP to arrive at the designated location. In addition, these conventional systems may require first moving a FOUP from the conveyor to a shelf adjacent a processing tool, and then from the shelf to a load port. This additional step imposes a time delay, or limits access to, the load ports—which reduces the system's maximum container throughput.
Therefore, there is a need for a conveyor buffer system whereby FOUPs located on the buffer system may be randomly accessed. There is also a need for a tool loading device that transports a FOUP from the conveyor directly to a load port of a processing tool.